Dry vacuum scroll pump

ABSTRACT

A dry scroll vacuum pump includes a fixed scroll, a drive shaft having an axis and an eccentric shaft portion, an orbiting scroll connected to the eccentric shaft portion so that during use rotation of the shaft imparts an orbiting motion to the orbiting scroll relative to the fixed scroll for pumping gas between a mechanism inlet and a mechanism outlet of a scroll mechanism comprising the scrolls; an inlet vacuum region for conveying gas from the pump inlet to the mechanism inlet; a cooling flow path formed inside the orbiting scroll for guiding a cooling fluid for cooling the orbiting scroll, the cooling flow path having a fluid inlet; and a sealing arrangement for sealing the fluid inlet from the inlet vacuum region so a cooling fluid can be conveyed across the inlet vacuum region through the sealing arrangement to the fluid inlet.

CROSS-REFERENCE OF RELATED APPLICATION

This application is a Section 371 National Stage Application ofInternational Application No. PCT/GB2016/053528, filed Nov. 10, 2016,which is incorporated by reference in its entirety and published as WO2017/089745 A1 on Jun. 1, 2017 and which claims priority of BritishApplication No. 1520878.8, filed Nov. 26, 2015.

FIELD

Embodiments relate to a dry vacuum scroll pump and to cooling of thepump.

BACKGROUND

A scroll vacuum pump comprises a pump housing which houses thecomponents of the pump. A fixed scroll is fixed relative to the pumphousing. A drive shaft has a concentric shaft portion and an eccentricshaft portion and an orbiting scroll is connected to the eccentric shaftportion so that during use rotation of the shaft imparts an orbitingmotion to the orbiting scroll relative to the fixed scroll for pumpingfluid between an inlet and an outlet of a scroll mechanism comprisingthe scrolls.

Gas enters the pumping mechanism through the inlet and is trapped in gaspockets between the scrolls. As the orbiting scroll orbits relative tothe fixed scroll these pockets are urged about a spiral or involute pathtowards a central outlet of the mechanism gradually reducing in size andachieving compression. A by-product of compression and operation of thepumping components is heat energy which may accumulate in the scrollsand a bearing mechanism of the pump degrading performance.

The discussion above is merely provided for general backgroundinformation and is not intended to be used as an aid in determining thescope of the claimed subject matter. The claimed subject matter is notlimited to implementations that solve any or all disadvantages noted inthe background.

SUMMARY

The embodiments provide a dry scroll vacuum pump comprising: a pumphousing having a housing inlet and a housing outlet; a fixed scrollfixed relative to the pump housing; a drive shaft having an axis and aneccentric shaft portion; an orbiting scroll connected to the eccentricshaft portion so that during use rotation of the shaft imparts anorbiting motion to the orbiting scroll relative to the fixed scroll forpumping gas between a mechanism inlet and a mechanism outlet of a scrollmechanism comprising the scrolls; an inlet vacuum region at inletpressure within the pump housing for conveying gas from the pump inletto the mechanism inlet during said orbiting motion; a cooling flow pathformed inside the orbiting scroll for guiding flow of a cooling fluidfor cooling the orbiting scroll, the cooling flow path having a fluidinlet located in the inlet vacuum region; and a sealing arrangement forsealing the fluid inlet from the inlet vacuum region so that coolingfluid can be conveyed across the inlet vacuum region through the sealingarrangement to the fluid inlet.

Preferably, the cooling fluid is low vacuum and may be at or in theregion of atmospheric pressure for example between about 1.5 bar and 0.5bar and preferably between 1.2 and 1.0 bar. In this arrangement, theatmospheric cooling fluid is conveyed across the inlet vacuum region tothe fluid inlet, even though the orbiting scroll is in motion within theinlet vacuum region.

The cooling flow path may have a fluid outlet located in the inletvacuum region and the sealing arrangement seals the fluid outlet fromthe inlet vacuum region so that low vacuum cooling fluid can be conveyedacross the inlet vacuum region through the sealing arrangement to thefluid outlet.

There is preferably a reverse scroll arrangement wherein the fixedscroll has an opening through which the shaft extends and is connectedto the orbiting scroll with the orbiting scroll on an opposing side ofthe fixed scroll to a drive motor, and the inlet vacuum region islocated adjacent the orbiting scroll.

In one example, the sealing arrangement has an inlet seal having a firstinlet portion fixed at the fluid inlet of the orbiting scroll, a secondinlet portion fixed relative to a pump housing fluid inlet through whichcooling fluid is conveyed, and a connecting inlet portion which isflexible to allow relative orbiting motion between the first inletportion and the second inlet portion during movement of the orbitingscroll in two orthogonal dimensions with respect to the axis.

Preferably, the sealing arrangement has an outlet seal having a firstoutlet portion fixed at the fluid outlet of the orbiting scroll, asecond outlet portion fixed relative to a pump housing fluid outletthrough which cooling fluid is conveyed, and a connecting outlet portionwhich is flexible to allow relative orbiting motion between the firstoutlet portion and the second outlet portion during movement of theorbiting scroll in two orthogonal dimensions with respect to the axis.

The inlet and/or outlet seal may comprise a gaiter seal.

The source of cooling fluid may be configured for conveying coolingfluid through the cooling flow path of the orbiting scroll, and may formpart of the scroll pump, or be a separate component from the pump, or agas line. The flow source may comprise a mechanical fan rotated by thedrive shaft. The source of cooling fluid may comprise a pump external tothe pump housing for conveying cooling fluid through the cooling flowpath. In other arrangements, the source of cooling fluid may be causedby motion of the fluid inlet to convey cooling fluid through the coolingpath.

The cooling flow path may be formed by casting within the orbitingscroll during manufacture.

it is preferable that the cooling flow path has a tortuous configurationwithin the orbiting scroll.

The cooling fluid may be air or water or another fluid, and may becooled to lower than ambient temperature prior to introduction.

The Summary is provided to introduce a selection of concepts in asimplified form that are further described in the Detail Description.This summary is not intended to identify key features or essentialfeatures of the claimed subject matter, nor is it intended to he used asan aid in determining the scope of the claimed subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the present invention may be well understood, anembodiment thereof, which is given by way of example only, will now bedescribed in more detail with reference to the accompanying drawings, inwhich:

FIG. 1 is a schematic representation of a dry scroll vacuum pump;

FIG. 2 shows one view of an orbiting scroll of the pump shown in FIG. 1;and

FIG. 3 shows another view of an orbiting scroll of the pump shown inFIG. 1.

DETAILED DESCRIPTION

Referring to FIG. 1, the pump 10 comprises a pump housing 12 and a driveshaft 14 having an eccentric shaft portion 16. The shaft 14 is driven bya motor 18 and the eccentric shaft portion is connected to an orbitingscroll 20 so that during use rotation of the shaft imparts an orbitingmotion to the orbiting scroll relative to a fixed scroll 22 for pumpingfluid along a fluid flow path between a pump housing inlet 24 and pumphousing outlet 26 of the compressor. The fixed scroll is shown generallyon the left and the orbiting scroll is shown generally on the right inFIG. 1 (i.e. the fixed scroll plate is on the left and the orbitingscroll plate is on the right as shown whilst the fixed and orbitingscroll walls overlap in the axial direction). In this reverse scrollarrangement, the fixed scroll comprises an opening 28 through which theshaft 14 extends and is connected to the orbiting scroll 20 so that theorbiting scroll is located an opposing side of the fixed scroll to themotor 18. A high, or inlet, vacuum region 30 is located at the inlet 24and a low vacuum, or outlet, region 32 is located at the outlet 26. Thehigh vacuum region is at inlet pressure. The low vacuum region is atexhaust pressure. In this way, the scroll arrangement is reversedcompared to a typical scroll pump in which the orbiting scroll is on thesame side of the fixed scroll as the motor.

A first bearing 34 supports the concentric portion of the drive shaft 14for rotation. The bearing 34 is fixed relative to the housing or asshown the fixed scroll 22. A second bearing 36 connects the eccentricportion 16 of the drive shaft to the orbiting scroll 20 allowingorbiting movement of the orbiting scroll relative to the eccentricportion. A first shaft seal 38 may be provided to resist the passage oflubricant from first bearing 34 towards an interface 40 between theorbiting scroll 20 and the fixed scroll 22 and a second shaft seal 42resists the passage of lubricant from second bearing 36 to theinterface. The shaft seals resist lubricant entering and mixing with thepumped gasses.

A counter-weight 44 balances the weight of the orbiting components ofthe pump, including the orbiting scroll 20, the second bearing 36 andthe eccentric portion 16 of the drive shaft. The orbiting scroll 20constitutes the majority of the weight of the orbiting components andits centre of mass is located relatively close to the scroll plate ofthe orbiting scroll. A cap 46 is fixed to a raised seat 48 of theorbiting scroll and seals the low vacuum region, containing thecounter-weight and the bearings 34, 36 from the high vacuum region 30.

An anti-rotation device 50 is located in the high vacuum region 30 ofthe pump and is connected to the orbiting scroll 20 and the housing 12.The anti-rotation device resists rotation of the orbiting scroll butallows orbiting motion of the orbiting scroll. The anti-rotation deviceis lubricant free and in this example is made from a plastics material,and may be a one-piece polymer component.

A flow source of cooling fluid in the form of a mechanical fan 52 ismounted to the drive shaft 14 for rotation when the drive shaft isdriven by the motor 18. Rotation of the fan causes flow of cooling fluid(typically ambient air) over the fixed scroll for cooling the fixedscroll. However, in a reverse scroll arrangement the orbiting scroll ison a distal side of the fixed scroll and therefore not physicallyexposed to coolant. Also the orbiting scroll is located in the highvacuum, or inlet, region 30 which means that there is less gas availablefor the convection of heat energy away from the orbiting scroll.

The amount of heat produced correlates with the amount of gas which ispumped. Therefore if throughput is increased more gas is compressed andgreater energy is lost in the form of heat, particularly at higherpressures closer to atmosphere if the pump is used for roughing. Aroughing pump may for example have an inlet pressure of between about500 mbar and 1 mbar and exhaust pressure at or around atmosphere. Aroughing pump may be used for example in the food packaging industry orfor paper handling. However, the invention can also be used in lowerpressure regimes (less than 1 mbar e.g. 10-2 and 10-3 mbar) for examplefor scientific instruments, since there is a trend to increase gasthroughput in such instruments thereby contributing to increased heatproduction.

Purely as examples a low throughput for pumping may be 500 to 1000 sccm(standard cubic centimetres per minute) and a high throughput may begreater than 50 slm (standard litres per minute).

Increased pump operating temperatures are not desirable since amongstother things they decrease an operative life of the pump, cause anincreased requirement for maintenance and potentially result in failure.The bearing mechanism is a key component of the pump and increased heatdeteriorates the mechanism. For example, a 10° C. rise in temperaturereduces the life of grease (lubricant) in the bearings by half (byaround 50%). Increased temperature causes expansion of bearingcomponents (and scroll members) reducing the fit between componentsdecreasing pumping efficiency and potentially causing contact betweenmoving surfaces. Additionally, tip seal wear increases with increasedtemperature. The production of tip seal dust causes contamination ofclean pumped environments. Tip seal dust is a particular problem inscientific instruments and silicon wafer processing and also in foodpackaging.

In dry pumping no lubricant is used in the pumping chamber of the scrollmechanism along the flow path for pumping. It is used outside thepumping chamber in the bearing mechanism. Lubricant in the chamber wouldin a lubricated pump provide a sealing function in addition tolubricating the interface between the scrolls, however it is a source ofcontamination and additional expense. Dry pumping is preferable in manycircumstances, such as for pumping a clean environment or production ofcomestible products. One disadvantage to dry pumping is that thecirculation of lubricant removes heat from a pumping mechanism, andtherefore a dry pump is more susceptible to overheating.

As briefly explained above, the problem of scroll member heating isparticularly acute in a reverse scroll vacuum pump where the orbitingscroll is located in the vacuum region of the pump. Notwithstanding, theinvention has applicability to normal scroll arrangements. The reverseconfiguration has certain advantages over a normal scroll, includingthat it is more compact (e.g. axially shorter) and does not require a“bellows” fixed to the orbiting scroll. A bellows acts as a seal forsealing an atmospheric and lubricated region of the pump from a vacuumregion and also resists rotation of the orbiting scroll. The provisionof bellows increases both axial length and radial width of the pump.

As indicated above the orbiting scroll is at least partially envelopedin low pressure gas and therefore heat is not easily dissipated from thescroll. Instead an atmospheric gas or liquid is required as a coolingagent. A difficulty arises in exposing the orbiting scroll to anatmospheric fluid because it is located in the vacuum region andadditional because it is not stationary.

In the present invention a cooling flow path for coolant is formed inthe body (principally in the plate) of the orbiting scroll for receivinga cooling agent. The cooling agent is a fluid at or around atmosphere orambient pressure or a small amount above atmosphere or ambient (e.g.between about 1.5 bar and 0.5 bar, or preferably between about 1.0 and1.2 bar sufficient to cause flow along the cooling flow path). Thecooling agent, or fluid, may be ambient air or a liquid such as water.The cooling agent may be pre-cooled or at ambient temperature, but ineither case below the temperature of the orbiting scroll to cause heatexchange from the orbiting scroll to the cooling fluid.

Reference is now made to FIG. 2 which shows a scroll mechanism 60 andcooling arrangement 62 in more detail. FIG. 2 is a simplifiedrepresentation for explanatory purposes only and omits components of thepump such as the bearing mechanism, cap and anti-rotation device.

A pump housing inlet 24 is in fluid communication with the high vacuum,or inlet, region 30 into which gas is pumped at low pressure (at anypressure between about 500 mbar and 10⁻³ mbar, or even lower, dependingon pumping requirements). The high vacuum region is in fluidcommunication with an inlet 25 of the scroll mechanism through which lowpressure gas is drawn from the high vacuum region and compressed by thescroll mechanism. The pump inlet 24 is not connected directly to thescroll mechanism inlet 25 because the orbiting scroll 22 is notstationary during pumping. In this regard, the drive shaft 14 has acentral rotational axis 70. The eccentric portion 16 of the shaft has acentral longitudinal line 72 offset from axis 70 by a distance OS.Depending on the size and rating of the scroll pump OS may be betweenabout 10 mm and 50 mm. The orbiting scroll 22, which is connected to theeccentric portion, is driven by the drive shaft to orbit with respect toaxis 70 in a plane orthogonal to the axis. As viewed in FIG. 2, theorbiting scroll moves about the axis in two orthogonal dimensions (i.e.upwards and downwards and into and out of the page in the Figure) by anamount equal to OS relative to the axis 70, or by an amount 2OS relativeto the pump housing.

The inlet 25 of the scroll mechanism 60 is in fluid communication with aradially outer wrap 27 of the scroll mechanism. Orbiting motion of theorbiting scroll causes fluid to be urged from the outer wrap 27 to aradially inner wrap 29. The inner wrap is in fluid communication with anoutlet 31 of the scroll mechanism. The low vacuum, or outlet, region 32within the pump housing is typically located in fluid communication withthe outlet of the scroll mechanism and outlet 26 of the pump housing(see FIG. 1). The low vacuum region 32 is separated and sealed from thehigh vacuum region 30 by the fixed scroll or the pump housing.

The low pressure pumped gas 64 is shown (represented by an X in acircle) located in the vacuum region 30 and partially enveloping thescroll mechanism 60. As shown in this example, the vacuum region 30 isdefined between the pump housing, the outer casing 66 of the orbitingscroll (and the cap 46 not shown in FIG. 2) and the outer casing 68 ofthe fixed scroll. Since the outer casing, or surface, 66 of the orbitingscroll is located in this high vacuum region heat does not easilydissipate from the orbiting scroll.

A cooling arrangement 62 is provided for cooling the orbiting scroll 22.Since the orbiting scroll is not stationary the cooling arrangementbridges the high vacuum region 30 to accommodate the orbiting motion ofthe orbiting scroll in order to supply a cooling fluid to a cooling flowpath in the orbiting scroll.

In more detail, a cooling flow path 74 is formed inside the orbitingscroll for guiding flow of a low vacuum, or atmospheric, cooling fluidfor cooling the orbiting scroll by heat exchange with the orbitingscroll. The flow path may be defined by one or more internal conduitscast into the orbiting scroll during casting, or manufacture, of theorbiting scroll or alternatively may be formed between two parts of theorbiting scroll which are subsequently fastened together and sealed.Other techniques may be used to form the flow path.

The cooling flow path has a fluid inlet 76 and a fluid outlet 78. Thefluid inlet and the fluid outlet may be positioned at diametricallyopposed parts of the orbiting scroll as shown, or more proximate oneanother. There may be more than one inlet or more than one outlet, andmore than one flow path, depending on cooling requirements. In the FIG.2 example, cooling fluid 80 (represented by symbol ‘0’) is caused toflow from outside the pump housing 12 through the fluid inlet 76, alongthe flow path 74 and subsequently through the fluid outlet 78 andoutside the pump housing. In this arrangement the cooling fluid mayconveniently be ambient air.

The fluid inlet 76 of the orbiting scroll 22 is connected to the pumphousing 12 by an inlet seal 82. The inlet seal has a first inlet portion90 fixed at the fluid inlet of the orbiting scroll and a second inletportion 92 fixed relative to a port 84 in the pump housing. The inletseal has an inlet connecting portion 94 which is sufficiently flexibleto allow relative motion between the first inlet portion and the secondinlet portion during motion of the orbiting scroll two dimensionsrelative to the axis 70. The fluid outlet 78 of the orbiting scroll isconnected to the pump housing 12 by an outlet seal 83. The outlet sealhas a first outlet portion 96 fixed at the fluid outlet of the orbitingscroll and a second portion 98 fixed relative to a port 79 in the pumphousing. The outlet sealing arrangement also has a connecting portion100 which is sufficiently flexible to allow relative motion between thefirst portion and the second portion during motion of the orbitingscroll.

The orbiting scroll of the scroll pumping mechanism orbits relative tothe fixed scroll to form gas pockets between the scroll walls which aregradually compressed during orbiting motion as the pockets are urgedfrom the radially outer inlet of the mechanism towards the centraloutlet. The orbiting motion causes the orbiting scroll to follow acircular path in a plane orthogonal to the axis of the drive shaft.Therefore the cooling fluid inlet 76 and the cooling fluid outlet 78 ofthe orbiting scroll move in circular paths relative to housing ports 84and 79, respectively. This circular movement constitutes movement in twodimensions in the plane orthogonal to the axis 70 (i.e. as shown towardsand away from the housing ports, and into and out of the page). Thecircular movement typically has a radius OS of between about 10-50 mm.The sealing arrangements are therefore required to be compressed andexpand by an amount twice OS and to bend in a lateral (axial) dimensionby an amount OS. At high pump rotational speeds (e.g. 60 Hz) significantphysical stresses and strains are applied to the sealing arrangements82, 83. The sealing arrangements must accommodate the physical impact ofthis movement over prolonged durations (e.g. for several weeks ofconstant use between maintenance operations).

In the example shown in FIG. 2, the sealing arrangements are formed bygasket seals having a pleated configuration. The sealing arrangementsare preferably made from a plastics or rubber having materialcharacteristics which tolerate such movement at typical rotationalspeeds for prolonged periods. It will also be appreciated that it may bedesirable to keep the pump as compact as possible and therefore tominimize the spacing between the housing ports 79, 84 and the fluidinlet/outlet 76, 78. In this case, the sealing arrangements are requiredto expand and contract by many times their own length. For example, ifOS is 50 mm and the minimum such spacing is 10 mm, the length of thesealing arrangements would vary from 10 mm to 110 mm. If OS is 10 mm andthe minimum such spacing is 10 mm, the length of the sealingarrangements would vary from 10 mm to 30 mm. Clearly other possibledimensions may be used depending pump configuration and intended use andthe sealing arrangements are required to accommodate such variation oflength from a compacted to expanded length by at least a factor of twoor (3 or 11 in the examples given above). A gasket as shown has beenfound to have a suitable configuration in this regard.

FIG. 3 is a cross-section through the orbiting scroll showing thecooling flow path. The cooling flow path 74 guides cooling fluid 80 fromthe fluid inlet 76 to the fluid outlet 78 in the orbiting scroll 22.FIG. 3 shows only one example of the flow path, which in thisconfiguration is a single curvilinear flow path between the fluid inletand fluid outlet.

The configuration of the flow path is preferably such as to pass througha substantial volume of the orbiting scroll in order to exchange heatwith as much of the orbiting scroll as is practical. For example if thecross-sectional area through the orbiting scroll is X then the flow pathmay extend through 50% of X and preferably 75% of X. The flow path mayhave a path centre which extends in a single plane through the orbitingscroll (e.g. orthogonal to the pump axis 70) or the flow path may extendin more than one plane through the orbiting scroll.

In other arrangements, there is a differential distribution of heatthrough the orbiting scroll when in use and the flow path is configuredso that it can remove more heat from higher temperature parts of theorbiting scroll. In this regard, the flow path may be configured byvolume or by cross-sectional area or total cross-sectional area (ifthere is more than one flow path) such that more cooling fluid isexposed to higher temperature parts of the scroll so that flow isproportional with temperature.

For example, a radially inner part of the orbiting scroll is at higherpressure and a radially outer part is at lower pressure. Since more heatis generated at higher pressures the flow path may be configured tocause more flow per volume of the orbiting scroll (or heat exchange) inthe typically hotter radially inner part than the cooler radially outerpart, particularly as the radially inner part is proximate the bearingsso as to reduce transfer of heat to the lubricant.

The flow path may have a tortuous, labyrinthine, spiral or any otherconfiguration with multiple turns in order to penetrate through anincreased amount of the body of the scroll. A turn causes the fluid tochange direction of flow and may be a turn through 45 degrees, 90degrees, 135 degrees, 180 degrees or more, or any angle between. Achange of flow direction causes some turbulence for mixing the coolingfluid (i.e. within the flow path, hotter fluid adjacent a scroll surfaceis mixed with cooler fluid away from the scroll surface) and this mixingincreases heat exchange.

Referring again to FIG. 2, the source of cooling fluid 86 is a pump orfan external to the pump housing 12 for conveying cooling fluid throughthe cooling flow path 74. In an alternative arrangement, a mechanicalsource of cooling fluid may be driven by drive shaft 14, shown in FIG.1, for example fan 52. In this latter case, fan 52 may he in fluidcommunication with an outer sleeve of the housing for conveying coolingfluid along the cooling flow path.

In a further alternative, a cooling fluid may be caused to flow alongthe cooling flow path by virtue of the movement of the orbiting scroll,without or with the addition of a further source of cooling fluid. Thismovement may be sufficient in itself to create flow by the pumpingaction of the orbiting scroll relative to the pump housing, for exampleby causing turbulence at the inlet and outlet of the path.

It is an object of the invention to provide pump cooling.

Although elements have been shown or described as separate embodimentsabove, portions of each embodiment may be combined with all or part ofother embodiments described above.

Although the subject matter has been described in language specific tostructural features and/or methodological acts, it is to be understoodthat the subject matter defined in the appended claims is notnecessarily limited to the specific features or acts described above.Rather, the specific features and acts described above are described asexample forms of implementing the claims.

1. A dry scroll vacuum pump comprising: a pump housing having a housinginlet and a housing outlet; a fixed scroll fixed relative to the pumphousing; a drive shaft having an axis and an eccentric shaft portion; anorbiting scroll connected to the eccentric shaft portion so that duringuse rotation of the shaft imparts an orbiting motion to the orbitingscroll relative to the fixed scroll for pumping gas between a mechanisminlet and a mechanism outlet of a scroll mechanism comprising thescrolls; an inlet vacuum region at inlet pressure within the pumphousing for conveying gas from the pump inlet to the mechanism inletduring said orbiting motion; a cooling flow path formed inside theorbiting scroll for guiding flow of a cooling fluid for cooling theorbiting scroll, the cooling flow path having a fluid inlet located inthe inlet vacuum region; and a sealing arrangement for sealing the fluidinlet from the inlet vacuum region so a cooling fluid can be conveyedacross the inlet vacuum region through the sealing arrangement to thefluid inlet.
 2. The dry vacuum scroll pump as claimed in claim 1,wherein the cooling flow path has a fluid outlet located in the inletvacuum region and the sealing arrangement seals the fluid outlet fromthe inlet vacuum region so that low vacuum cooling fluid can be conveyedacross the inlet vacuum region through the sealing arrangement to thefluid outlet.
 3. The dry vacuum scroll pump as claimed in claim 1,having a reverse scroll arrangement wherein the fixed scroll has anopening through which the shaft extends and is connected to the orbitingscroll with the orbiting scroll on an opposing side of the fixed scrollto a drive motor, and the inlet vacuum region is located adjacent theorbiting scroll.
 4. The dry vacuum scroll pump as claimed in claim 1,wherein the sealing arrangement has an inlet seal having a first inletportion fixed at the fluid inlet of the orbiting scroll, a second inletportion fixed relative to a pump housing fluid inlet through whichcooling fluid is conveyed, and a connecting inlet portion which isflexible to allow relative orbiting motion between the first inletportion and the second inlet portion during movement of the orbitingscroll in two orthogonal dimensions with respect to the axis.
 5. The dryvacuum scroll pump as claimed in claim 1, wherein the sealingarrangement has an outlet seal having a first outlet portion fixed atthe fluid outlet of the orbiting scroll, a second outlet portion fixedrelative to a pump housing fluid outlet through which cooling fluid isconveyed, and a connecting outlet portion which is flexible to allowrelative orbiting motion between the first outlet portion and the secondoutlet portion during movement of the orbiting scroll in two orthogonaldimensions with respect to the axis.
 6. The dry vacuum scroll pump asclaimed in claim 4, wherein the inlet and/or outlet seal comprises agaiter seal.
 7. The dry vacuum scroll pump as claimed in claim 1,comprising a source of cooling fluid configured for conveying coolingfluid through the cooling flow path of the orbiting scroll.
 8. The dryvacuum scroll pump as claimed in claim 7, wherein the flow sourcecomprises a mechanical fan rotated by the drive shaft.
 9. The dry vacuumscroll pump as claimed in claim 1, wherein the source of cooling fluidcomprises a pump external to the pump housing for conveying coolingfluid through the cooling flow path.
 10. The dry vacuum scroll pump asclaimed in claim 1, wherein the source of cooling fluid is caused bymotion of the fluid inlet to convey cooling fluid through the coolingpath.
 11. The dry vacuum scroll pump as claimed in claim 1, wherein thecooling flow path is formed by casting within the orbiting scroll duringmanufacture.
 12. The dry vacuum scroll pump as claimed in claim 1,wherein the cooling flow path has a tortuous configuration within theorbiting scroll.
 13. The dry vacuum scroll pump as claimed in claim 1,wherein the cooling fluid is air or water.
 14. The dry vacuum scrollpump as claimed in claim 1, wherein the cooling fluid is at or in theregion of atmospheric pressure 1 bar to 0.5 bar and preferably 1.0 to1.2 bar.
 15. (canceled)